Method of producing compounds of the vitamin a series and intermediates for use therein



United States Patent METHOD OF PRODUCING COMPOUNDS OF THE VITAMIN A SERIES AND INTERMEDIATES FOR USE THEREIN Hendrick Evert van Geelen and Henri Pieter van Leeuwen, Van Houtenlaan, Weesp, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Application May 3, 1965, Ser. No. 452,875, which is a division of application Ser. No. 107,917, May 5, 1961. Divided and this application Aug. 24, 1966, Ser. No. 627,272

Claims priority, application Netherlands, May 6, 1960,

1 Claim. c1. 260464) ABSTRACT OF THE DISCLOSURE A step in the synthesis of vitamin A compounds wherein an imine of the vitamin A series is condensed with cyanoacetic acid or a derivative thereof to produce a nitrile carboxylic acid or a derivative thereof of the vitamin A senes.

This application is a division of application Ser. No. 452,875, filed May 3, 1965, and now U.S. Patent 3,330,843, said application Ser. No. 452,875 being a division of application Ser. No. 107,917, filed May 5, 1961 and now U.S. Patent 3,190,898.

This invention relates to the production of compounds of the vitamin A series and to novel intermediates for use therein.

As is known, in the synthesis of compounds having vitamin A activity which are characterized by the unsaturated aliphatic-alicyclic hydrocarbon group shown in formula:

one generally starts from a trimethylcyclohexene compound having a shorter side chain which is lengthened by one or more condensation reactions.

In this chain lengthening synthesis it is also known to use one or more Knoevenagel condensations of an aldehyde or a ketone from the vitamin A series with cyanoacetic acid or with an ester or amide of this acid.

It has, for example, been proposed to subject a solution of fi-ionone in acetic acid and benzene in the presence of ammonium acetate to a condensation with cyanoacetic acid or with an ester or amide of cyanoacetic acid, and a similar reaction has been described in which one starts from 5,;8-ionylidene-pent-3-enone-2, the so-called C ketone.

In this reaction, water is evolved which, in order to obtain a reaction yield, is removed by distillation together with acetic acid and benzene.

However, these reaction conditions, which for a Knoevenagel' condensation of an aldehyde or ketone with cyanoacetic acid or a derivative thereof generally produce good results, in the vitamin A series give rise to difficulty.

In building up the chain characteristic of vitamin A, it is essential that a correct arrangement of double bonds is obtained.

It has been found that, the yield of nitrile produced by decarboxylation of the primary condensation product is Patented Nov. 12, 1968 ice considerably reduced because of the formation of a considerable amount of isomerization products. It is considered that secondary reactions which involve shifting of double bonds are highly promoted by the presence of water of reaction in the boiling acetic acid reaction mixture. In addition, under these conditions, if the reaction is carried out with cyanoacetic acid, considerable decarboxylation occurs during the condensation reaction, which decarb oxylation under such conditions is accomplished by isomerization.

A principal object then of this invention is to provide a method for the production of vitamin. A compounds in which said isomerization is largely eliminated.

Another object of this invention is to provide new and novel intermediates for use in the improved method of this invention.

These and other objects of this invention will be apparent from the description that follows:

According to the invention the required lengthening of the carbon chain in the synthesis of vitamin A compounds is carried out by condensing an imine of the vitamin A series with the cyanoacetic acid or a derivative thereof instead of the corresponding aldehyde or ketone to produce a nitrile carboxylic acid or a nitrile carboxylic acid derivative.

The novel method of the invention greatly lessens the danger of isomerization because the reaction does not require the supplying of heat so that no boiling of an aqueous acid solution is required and no decarboxylation of the resultant nitrile carboxylic acid takes place.

If the nitrile carboxylic acid is produced by the method according to the present invention, a nitrile in the vitamin A series may be produced therefrom by a known method by decarboxylation in a medium in which no undesirable isomerization occurs.

The resulting nitrile may further be converted by known methods into compounds having vitamin A activity or into further intermediate products for the production of compounds having vitamin A activity.

More particularly, the invention relates to a condensation reaction of imines having the fomula in which formula R is hydrogen or a hydrocarbon radical, such as an alkyl, aralkylor aryl-group and n is 0 or 1 (representing B-ionone imines and fi-C ketone imines, respectively) with cyano-acetic acid or with an ester or an amide of this acid so that nitrile carboxylic acids or derivatives thereof are obtained.

In these imines the alkyl group represented by R may contain any number of carbon atoms and may range from methyl to hexadecyl. Also R may represent an aralkylor aryl-group such as a phenyl-, a benzylor a phenylethylgroup. However, most satisfactory results are obtained if R represents a lower alkyl group containing from 1 to 5 carbon atoms for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl and amyl.

Any ester of the cyano-acetic acid with a monohydric aliphatic alcohol may be employed for example the methyl, butyl, propyl, hexyl, octyl, dodecyl, vinyl and allyl esters as Well as benzyl, phenyl and cyclohexyl esters. These compounds may be converted by known methods by decarboxylation to nitriles of the vitamin A series which are particularly valuable as intermediate products for the production of compounds having vitamin A activity.

Thus, for example, the fi-ionylidene acetonitrile obtained after decarboxylation, if one starts from a fi-ionone imine, may be converted by known methods to [i-ionylidene acetaldimine, which after hydrolysis to fi-ionylidineacetaldehyde by condensation with acetone is converted to C ketone. The vitamin A acid nitrile obtained if one starts from a C ketone imine, may be converted by reduction and subsequent hydrolysis to the vitamin A aldehyde which has vitamin A activity in itself and may be further reduced to vitamin A alcohol.

Another important imine from the vitamin A series that can be used in the reaction according to the invention by condensing it with cyanoacetic acid or a derivative thereof is for example citraldimine. By condensing this aldimine with cyanoacetic acid the corresponding nitrile carboxylic acid citrylidene cyanoacetic acid is obtained. This nitrile carbonic acid also can be decarboxylated in a known manner to obtain the corresponding nitrile that is a valuable intermediate in the production of useful compounds in the vitamin A series.

The novel starting imines of the invention may be produced by known methods, for example by reacting aldehydes or ketones from the vitamin A series with ammonia or primary amines.

Preferably, the Schiffs bases of carbonyl compounds in the vitamin A series with primary amines are used as starting material, since they can the simply obtained in satisfactory yield.

Particularly good results are obtained if one starts from Schilfs bases of carbonyl compounds in the vitamin A series with aliphatic primary amines containing from 1 to carbon atoms, for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl or amyl amine.

The reaction of the imine with cyano-acetic acid or with an ester or amide of this acid is preferably carried out in a solvent, suitable solvents being others or aliphatic, alicyclic, aliphatic-alicyclic or aromatic hydrocarbons such as ether, benzene, hexane, petroleum ether, methylcyclohexane and cyclohexane. This reaction is preferably carried out at a temperature between 20 C. and 60 C.

The reaction of the imine with the free cyano-acetic acid is of particular importance since the nitrile carboxylic acid formed in this reaction can :be decarboxylated by known simple methods without risk of unwanted isomerisation.

The condensation reaction may be carried out by adding a solution of the cyano-acetic acid or of a derivative thereof to a solution of the imine or Vice versa. Preferably, an excess of cyano-acetic acid is used, for example an excess of from 10% to 200%.

When the reaction mixture has been stored for some time, for example at room temperature, the reaction product can be separated in a usual manner. The isolation of the nitrile carboxylic acid formed may, for example, be effected by pouring the mixture into dilute aqueous alcoholic solution, for example in 1 N solution of caustic soda. The water layer is separated, washed, for example with petroleum ether, and acidified, for example by the addition of an aqueous solution of a strong inorganic acid, for example hydrochloric acid or sulphuric acid. By means of a non-Water-miscible organic solvent, preferably a low-"boiling solvent, such as diethyl ether or petroleum ether the nitrile carboxylic acid is extracted from the acid aqueous solution, the extract is washed so as to be free from acid and subsequently the solvent is removed by evaporation, under reduced pressure, if required. By heating the resulting nitrile carboxylic acid either by itself or preferably in a solution in toluene or an organic base, for example in pyridine, collidine, triethyl amine or dimethyl aniline, in the presence of a copper compound, for example a cupric salt, such as cupric acetate, a nitrile in the vitamin A series is obtained in a particularly pure form.

The invention will now be described in greater detail with reference to the following examples:

EXAMPLE I 38.4 g. of .fl-ionone (0.2 mol) were dissolved in 200 cc. of anhydrous methanol saturated with ammonia. While the mixture was stirred and maintained at a temperature between 5 C. and 40 C. by cooling with ice, ammonia was passed through for several hours. The mixture was allowed to stand at room temperature for 2 days. It was then dried by evaporation in a vacuum at room temperature.

The residue, 38.1 g. of which owing to decomposition of the imine in the process of evaporation consisted partly of .fl-ionone-in the ultraviolet absorption spectrum (0.4 n-sulphuric acid ethanol solution) showed a maximum at 335 ru with an Eff of 600 This residue was dissolved in cc. of absolute diethyl ether to which a solution of 22.46 g. (0.265 mol) of dry cyano-acetic acid in 5 00 cc. of absolute ether was added. After standing for 2 days at room temperature, the reaction mixture was poured into a 1 N solution of caustic soda. The water layer was separated off, washed with petroleum ether and acidified with 10 N sulphuric acid.

The mixture was then extracted with ether, the ethereal extract washed with a common salt solution to remove the sulphuric acid and evaporated in a vacuum. 19.6 g. of fi-ionylidene cyanoacetic acid were obtained in the form of a yellow fine crystalline powder having an EF of 597 at 348 mp.

13 g. of this fl-ionylidene cyanoacetic acid were dissolved in 100 cc. of a saturated solution of cupric acetate in pyridine and the solution was boiled for three hours, then poured into water and extracted with petroleum ether. The extract was washed in succession with 2 N- hydrochloric acid, 2 N-solution of caustic soda and several times with water.

The petroleum ether was then removed by evaporation in a vacuum at 100 C. 11 g. of ,B-ionylidene acetonitrile were obtained having an Eif' value of 605 at 305 mu izm designates the value of the extinction of a 1% solution at a layer thickness of 1 cm.).

EXAMPLE II A solution of 38.4 g. (0.2 mol) ,B-ionone in 200 cc. of absolute ether and 17.7 g. of isopropylamine (0.3 mol) was allowed to stand at room temperature for 5 days. Silica gel was added in an amount suflicient to absorb the water evolved, that is to say, to permanent blueing, and filtered off after standing for 1 day.

To the resulting solution of .fl-ionone isopr-opyl imine was added a solution of 51 g. (0.6 mol) of dry cyanoacetic acid in cc. of absolute ether.

After standing for 3 days at room temperature, the reaction mixture was poured into a 1 N solution of caustic soda, the water layer washed with petroleum ether, acidified with 10 N sulphuric acid and extracted with ether. The ethereal extract was washed free from sulphuric acid with an aqueous common salt solution and then dried by evaporation in a vacuum at 10 C.

38.3 g. of fl-ionylidene cyanoacetic acid were obtained having an Eifig of 636 at 348 mu This product was decarboxylated in the manner described in Example I, 32.5 g. of fi-ionylidene acetonitrile being obtained having an EH5 value of 620 at 305 mu 5 EXAMPLE III 17.7 g. of n-propylamine were added to a solution of 38.4 gms. of fl-ionone in 2 cc. of absolute ether. After being allowed to stand for 5 days at room temperature, the mixture was dried by the addition of silica gel, which was filtered off after standing another day. The solution was then dried by evaporation in a vacuum at a temperature of from 50 C. to 60 C., 46.1 grns. of a viscous yellow oil being obtained having an The resultant imine was dissolved in 80 cc. of absolute ether, a solution of 35.7 g. of dry cyanoacetic acid (0.42 mol) in 200 cc. of absolute ether being added to this solution. During the addition of the two solutions so much reaction heat was evolved that the liquid lboiled.

After standing for 2 days at room temperature, the reaction mixture was poured into 1 N solution of caustic soda, the water layer was washed with petroleum ether and acidified with N sulphuric acid. The mixture was extracted with ether, the ethereal extract was washed free from sulphuric acid, dried and then evaporated. 33.6 g. of B-ionylidence cyanoacetic acid were obtained.

In the manner described in Example 1, this nitrile was decanboxylated so that a nitrile was produced having an EPZ of 639 at 305 mu EXAMPLE Iv cc. (0.0955 mol) of fi-ionone were added to 21 cc. of n-butylamine (0.208 mol) at room temperature, the temperature of the mixture rising to about C.

After allowing the mixture to stand at room temperature for 3 days, ccs. of petroleum ether (40-60) were added, the mixture then being dried by evaporation at 90 C.

22.88 gms., i.e. 0.0925 mol, of N-n, butyl 8 ionone imine were obtained.

E1 51 at 338 mu=697 Equivalent weight: Found: 258. Calculated: 247. After triple distillation,

}Zfm =737 and equivalent weight 252 This imine was treated in a manner entirely analogous to that described in the preceding example with cyanoacetic acid, very pure B-ionylidene cyanoacetic acid being obtained in a yield of 85%. In a second experiment, carried out in the same manner even a yield of 95.8% was obtained.

The B-ionylidene acetonitrile obtained therefrom by decarboxylation had an E1? value of 650 at 305 m EXAMPLE V To a solution of 0.1 mol N-Inethyl B-ionone imine obtained by reacting fi-ionone with methylamine in 100 ml. methanol 17 'g. dry cyanoacetic acid was added. The reaction mixture was kept at room temperature for 7 days. After this the mixture Was poured into 200 ml. 1 N solution of caustic soda. The alkaline mixture was extracted 3 times with petroleum ether (boiling point 40-60 C.). After acidifying the alkaline water layer by the addition of 30 ml. 10 N sulfuric acid. This aqueous liquid was twice extracted with 175 ml. diethylether. These ether extracts were combined and washed free from sulfuric acid and then dried by evaporation in vacuum. The residue was recrystallized from ethanol and a crystalline product,

fl-ionylidene cyanoacetic acid, was obtained with a melting point 172-l74 C. having an Ei'fi value of 670 at 345 m EXAMPLE VI To a solution of 0.1 mol N-n butyl 13 ionylidenepent 3 onimine 2 (N-n butyl ,8 C ketimine, obtained by reacting {3 ketone with a butylamine) in 50 ml. methanol a solution of 17 g. cyanoacetic acid in 50 ml. methanol was added. After stirring, the mixture was kept at room temperature for seven days. In a manner as described in Example V there was obtained from the reaction mixture the crystalline u-cyano vitamin A acid with a melting point of 185-186 C. and an Ei g value 1210 at 390 mu EXAMPLE VII 17 g. dry cyanoacetic acid was dissolved in ml. methanol. To this solution while stirring, there was added 0.1 mol N-rnethyl citraldimine obtained. by reacting citral with methylamine. The mixture was kept at room temperature during 1 hour and after this in a similar manner as described in Example V a crystalline product, citrylidene cyanoacetic acid, melting point -121 C. with an Elz value 1160 at 302 mg was obtained from it.

EXAMPLE VIII In exactly the same manner as described in Example VII N-n butylcitraldimine was reacted with cyanoacetic acid and citrylidene cyanoacetic acid was obtained.

What is claimed is:

1. A method of preparing a nitrile derivative of the vitamin A-series, having the structural formula comprising condensing, at a temperature between about 20 C. and 60 C., an imine of the formula 0H=c H-c'J=NR CH3 CH3 with a compound of the formula in which formula R is a member of the group consisting of hydroxyl, alkoxyl and NH and R is a member of the group consisting of hydrogen and hydrocarbon radicals.

References Cited UNITED STATES PATENTS 3,157,660 11/ 1964 Stilz et al 260-464 XR 3,219,696 1 1/ 1965 Van Geelen 260-464 XR 3,244,741 4/1966 Zeven Huizen 260-464 3,247,239 4/ 1966 Truscheit et al. 260--464 XR OTHER REFERENCES 'Hauser et al., J.A.C.S., 62, pp. 2389-2392, (1940) QD-l-AS.

JOSEPH P. BRUST, Primary Examiner. 

